Messages in this thread | | | Date | Mon, 22 Oct 2018 17:24:07 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH RFC kenrel/rcu] Eliminate BUG_ON() for sync.c |
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On 10/22, Paul E. McKenney wrote: > > The sync.c file has a number of calls to BUG_ON(), which panics the > kernel, which is not a good
Agreed.
I added these BUG_ON's for documentation when I was prototyping this code, perhaps we can simply remove them.
> @@ -125,12 +125,12 @@ void rcu_sync_enter(struct rcu_sync *rsp) > rsp->gp_state = GP_PENDING; > spin_unlock_irq(&rsp->rss_lock); > > - BUG_ON(need_wait && need_sync); > - > if (need_sync) { > gp_ops[rsp->gp_type].sync(); > rsp->gp_state = GP_PASSED; > wake_up_all(&rsp->gp_wait); > + if (WARN_ON_ONCE(need_wait)) > + wait_event(rsp->gp_wait, rsp->gp_state == GP_PASSED);
This wait_event(gp_state == GP_PASSED) is pointless, note that this branch does gp_state = GP_PASSED 2 lines above.
And if we add WARN_ON_ONCE(need_wait), then we should probably also add WARN_ON_ONCE(need_sync) into the next "if (need_wait)" branch just for symmetry.
So I'd suggest to either turn that BUG_ON(need_wait && need_sync) above into WARN_ON_ONCE(wait && sync) or simply remove it.
Again, the only purpose of this BUG_ON() is to explain to the reader that it is not (must not be) possible that, say, gp_state == GP_IDLE while gp_count != 0.
---------------------------------------------------------------------------- Damn.
This suddenly reminds me that I rewrote this code completely, and you even reviewed the new implementation and (iirc) acked it!
However, I failed to force myself to rewrite the comments, and that is why I didn't send the "official" patch :/
May be some time...
Oleg.
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